Effective host immunity to Mycobacterium tuberculosis is dependent on T cell-mediated responses against antigens of the bacillus. Our recent work has shown that M.tuberculosis encodes In its genome pathways that promote evasion or subversion of host immunity, and that these interfere with effective vaccination by live, attenuated mycobacterial strains. In previous work, we have identified multiple immune evasion genes and have demonstrated that their inactivation or deletion can lead to more immunogenic, attenuated live mycobacterial vaccines. In this project, we will build on this background to develop novel live M. tuberculosis strains that generate enhanced T cell responses and more robust protective immunity in infected animals. Mutations will also be introduced to eliminate virulence even in the setting of immunodeficiency, thus creating vaccine strains that will in principle be safe for widespread use in human populations. In addition, we will use the incorporation of chemical adjuvant into live mycobacterial vaccine strains and several approaches to boosting of secondary responses to further enhance vaccine-induced protection against tuberculosis. Three specific aims are proposed: 1) Assess the impact of mutations In M. tuberculosis that enhance apoptosis of infected host cells on T cell responses; 2) Identify and characterize mutants of M. tuberculosis that enhance antigen presentation by MHC class 11; 3) Combine genetic modifications with chemical adjuvant and boosting strategies to enhance T cell response and protective efficacy induced by attenuated M. tuberculosis vaccine strains. The long term goal of these studies is to establish principles that will lead to safer and more effective live M. tuberculosis vaccines that will contribute to controlling the global burden of tuberculosis and to reducing the emergence of multidrug resistant strains. This project relates to the overall goals of this program project by seeking to improve the immunogenicity of live attenuated M. tuberculosis vaccines, and by establishing correlates of protection through the analysis of specific cellular immune responses. Extensive interactions with other components of the P01 funded program are proposed, and the project will benefit significantly from the various core resources supported by the P01.